thiolliere / pallet-stablecoin

a sample implementation of a non-collateralized stablecoin on substrate

pallet-stablecoin = '0.0.6'

Note: Not published to crates.io

Stablecoin example pallet

This is a substrate pallet showcasing a sample implementation of a non-collateralized stablecoin based on the Basis Whitepaper.

Note: Example project for illustration, NOT audited and NOT production ready.

Dependencies

This pallet depends on an external implementation of its FetchPrice trait - for example by an offchain worker - to act as a price oracle.

Installation

Runtime Cargo.toml

To add this pallet to your runtime, simply include the following in your runtime's Cargo.toml file:

[dependencies.pallet-stablecoin]
default_features = false
git = 'https://github.com/apopiak/pallet-stablecoin.git'

and update your runtime's std feature to include this pallet's std feature:

std = [
    # --snip--
    'pallet_stablecoin/std',
]

Runtime lib.rs

Here is an example imlementation of its trait:

use pallet_stablecoin::Coins;

parameter_types! {
    pub const ExpirationPeriod: BlockNumber = 5 * 365 * DAYS; // 5 years = 5 * 365 * DAYS
    pub const MaximumBids: usize = 1_000;
    pub const MinimumBondPrice: Perbill = Perbill::from_percent(10);
    pub const AdjustmentFrequency: BlockNumber = 1 * MINUTES; // 1 minute = 60000 / MILLISECS_PER_BLOCK
    pub const BaseUnit: Coins = 1_000_000;
    pub const InitialSupply: Coins = 1000 * BaseUnit::get();
    pub const MinimumSupply: Coins = BaseUnit::get();
}

impl pallet_stablecoin::Trait for Runtime {
    type Event = Event;

    type CoinPrice = some_price_oracle::Module<Runtime>;
    type ExpirationPeriod = ExpirationPeriod;
    type MaximumBids = MaximumBids;
    type MinimumBondPrice = MinimumBondPrice;
    type AdjustmentFrequency = AdjustmentFrequency;
    type BaseUnit = BaseUnit;
    type InitialSupply = InitialSupply;
    type MinimumSupply = MinimumSupply;
}

and include it in your construct_runtime! macro:

Stablecoin: pallet_stablecoin::{Module, Call, Storage, Event<T>},

GenesisConfig chain_spec.rs

Runtimes using the pallet need to add the StablecoinConfig to their genesis config. The config expects a Vec(AccountId, u64) to initialize the shareholders. See the following snippet for an example:

use node_template_runtime::{ // ... other imports
    StablecoinConfig
};
// ...

    GenesisConfig {
        system: Some(SystemConfig { /* elided */ }),
        // ... other configs
        stablecoin: Some(StablecoinConfig {
			shareholders: endowed_accounts.iter().cloned().map(|acc| (acc, 1)).collect(),
        }),
    }

With this config the endowed accounts will be the shareholders of the stablecoin.

Implementation

The implementation follows the Basis Whitepaper. (It also takes some inspiration from this unfinished Solidity implementation.)

• Basis tokens are called Coins and represent an ERC20-like token that will be stabilized by increasing and decreasing supply.
• Bond tokens are called Bonds and allow in- and decreasing the supply. They represent a promise for n Coins in the future (under certain conditions).
• Share tokens are called Shares and have a supply fixed at initialization time of the stablecoin. If there are not enough Bonds to increase coin supply, Coins are distributed to the accounts holding shares.

The ExpirationPeriod is configurable and measured in blocks (type BlockNumber).

The continuous bidding auction for bonds is implemented as a bounded priority queue to reduce storage costs. The paper does not specify whether it should or should not be bounded.

Reference Docs

You can view the reference docs for this pallet by running:

cargo doc --open